Optical spectral weights and the ferromagnetic transition temperature of colossal-magnetoresistance manganites: Relevance of double exchange to real materials

Abstract

We present a thorough and quantitative comparison of double-exchange models to experimental data on the colossal magnetoresistance manganese perovskites. Our results settle a controversy by showing that physics beyond double-exchange is important even in La0.7Sr0.3MnO3, which has been regarded as a conventional double-exchange system. We show that the crucial quantity for comparisons of different calculations to each other and to data is the conduction band kinetic energy K, which is insensitive to the details of the band structure and can be experimentally determined from optical conductivity measurements. The seemingly complicated dependence of Tc on the Hund's coupling J and carrier concentration n is shown to reflect the variation of K with J, n and temperature. We present results for the optical conductivity which allow interpretation of experiments and show that a feature previously interpreted in terms of the Hund's coupling was misidentified. We also correct minor errors in the phase diagram presented in previous work.

Transport properties of diluted magnetic semiconductors: Dynamical mean-field theory and Boltzmann theory

“…(15), but for the Bethe lattice the explicit form is derived in ref. 19. The dc-resistivity ρ = 1/σ dc is then found from Eq.…”

“…is the spectral function, Φ(ε) = (4t 2 − ε 2 )/3 is the current vertex for the Bethe lattice 19 , f (ω) is the Fermi distribution function. For the hypercubic lattice 18 Φ(ε) = 1 has been used in Eq.…”

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

“…The spectral weight in the optical spectroscopy is determined by the kinetic energy, 45 and reflects the onset of magnetic order 46,47 and/or orbital order. 48 As shown by Ahn and Millis,47 in the weak coupling regime one can analyze the total spectral weight in optical absorption using the HartreeFock approximation for the relevant tight-binding Hamiltonian.…”

Transport Properties of Correlated Electrons in High Dimensions

“…al [11] overlooked violations of the hc f -sum rule. All previous approaches specific to the Bethe DOS were associated with anisotropic or incoherent transport; the most interesting of these [4,6] have not yet been linked rigorously to microscopic models. Our method yields the first derivation for σ(ω) consistent with a semielliptic DOS that implies isotropic transport which is fully coherent in the noninteracting limit.…”

“…A derivation of σ(ω) directly for the Bethe tree (using the level-picture Fig. 1a) by Chung and Freericks [4] is still incomplete [5]; up to a factor of 3, the same expressionρ(ǫ) ∝ (4 − ǫ 2 )ρ(ǫ) was obtained [6] in a heuristic scheme by enforcing the hc f -sum rule (4). An alternative direct approach [7] fails to describe the coherent transport expected in the metallic regime.…”